1. Technical Field
The present subject matter relates to techniques and equipment for finding the position of RF wireless devices.
2. The Prior Art
The most widely used position location technique for geoposition location of mobile wireless stations is the hyperbolic position location technique, commonly known as the time difference of arrival (TDOA) position location method. This technique utilizes cross-correlation methods to calculate the difference in time of arrival (TOA) of a transmitted signal from a Wireless Station to a number of sensors. By measuring the differential delay of the waveforms arriving to the different sensor locations, a set of parabolic surfaces can be constructed which satisfy the differential propagation measurements from the source to each possible pair of sensors. The intersection of these parabolic surfaces dictates possible locations of the source. These intersections, whether among each other or with known surfaces as for example the plane denoting the earth surface, render parabolas which can be used to determine the most likely geolocation of the emitted signal. There are currently a number of well known techniques which minimize different metrics in order to determine the most likely emitter location.
Currently, whether the sensors are mobile or not, the process for locating an emitter is based on taking a sufficient number of measurements at the same time and at different position locations before using those measurements to estimate an emitters' position location. The problem with this is that for any reasonably good accuracy, one needs a considerable number of sensors. The number of sensors needs to be greater or equal to three in order to locate an emitter without uncertainty. In reality, four sensors are needed to derive elevation estimates which will be needed in situations where the emitter is located in hilly or mountainous terrain. In actual systems, the number of sensors needed is much higher than three or four in order to provide accurate enough position location estimates.